This invention is directed to tools for installation of electrical equipment, and is more specifically directed to wrenches for tightening the lock nuts that are employed for securing metal (or non-metal) electrical conduit to a metal electrical junction box. The invention is more particularly concerned with a hand tool that facilitates the speedy and efficient installation of electrical work in conduit.
Electrical power is provided through metal conduit for industrial, commercial and residential installations. The metal conduit connects into a metal electrical box, i.e., junction box, fuse or breaker box, or the like, and a circular penetration (e.g., a knock-out) is provided in the box, with the conduit passing through this and being secured to the box with threaded metal fasteners. Lock nuts are used as the fasteners on the inside of the box, and these have some structure on them that penetrates the paint or other coating on the box when the nut is installed as the means for completing the ground path between the conduit and the box. The typical lock nut has an annular body with a female-threaded round opening that screws onto the male thread provided on the end of the conduit, and a number of ears or lugs that radiate out from the annular body. The electrician installs these on the conduit and turns them down by hand. Then the electrician has to secure them by using a tool, and as often as not this tool is a screwdriver that is placed against one of the lugs and is hammered to turn the lock nut. It would be more efficient, and safer, if a wrench were provided to apply torque to the lock nuts, but these have not been available to the electrician.
There have; been some wrenches proposed in the prior art, but they have had only limited success, and are not now commercially available. These earlier wrenches include a conduit wrench as described in Rose U.S. Pat. No. 1,972,239; a junction box wrench as described in Houghton U.S. Pat. No. 2,522,038; a square-drive lock-nut wrench as shown in Barnes U.S. Pat. No. 3,768,345; a wrench-like lock-nut tool as described in Takas U.S. Pat. No. 5,524,511; and a double-ended open lock-nut wrench as shown in Howard U.S. Des. Pat. No. Des. 379,053. These tools have not proved to be practicable, or else have been too expensive to manufacture. Instead it is desired to have a simple tool that can be used with a variety of styles of lock nut, and which the electrician can easily and securely set onto the lock nut and rotate without slipping off.
Accordingly, it is an object to provide the lock nut wrench of an improved design that is simple to use and is relatively inexpensive to manufacture, and which facilitates secure engagement of the lock nuts onto the conduit and electrical junction box.
It is another object to provide a lock nut wrench that can be used easily with either six- or eight-lug lock nuts.
It is a further object to provide a lock nut wrench that helps the electrician in the case that the tool contacts a live (electrified) metal surface.
According to an aspect of this invention, a lock-nut wrench is provided for tightening the lock nuts that secure a metal conduit to a metal electrical junction box. As aforementioned, the typical lock nuts have a generally annular, i.e., cylindrical body with a female thread that engages a male thread on the conduit and a plurality of regularly spaced, outward, radially-directed lugs. At least some of the lock-nut lugs or ears have a foot or edge that cuts into the metal wall of the electrical box when the lock nut is rotated tight on the conduit, to complete the ground path between the conduit and the box. The lock-nut wrench of this invention has an elongated handle that is adapted to be gripped by the electrician, and a head at one end of the handle or else first and second heads at opposite ends of the handle. The head or heads have right and left arcuate jaws with distal ends that define an opening or gap of sufficient size to pass over the associated conduit. Each jaw has a first radially inwardly directed tooth at its distal end and a second radially inwardly directed tooth spaced proximally or back from it; the first and second teeth of each jaw defining between them a space to accommodate one lug of the lock nut. The resulting spaces on each head are 180 degrees apart, to capture the two 180-degree opposed lugs of the lock nut. There can be an offset where each head is joined to the handle, so that the handle and the head lie in parallel planes, or with the handle having a moderate amount of tilt. This facilitates reaching lock nuts at surfaces that may be below or behind a flange or lip at the front or open side of the junction box. In a preferred embodiment, the inside of the head, that is, the remainder of the jaws proximal of the second teeth, is free of further teeth and define a cylindrical surface that matches the radial outer extent of at least one lug of the lock nut. The handle may connect to the center of the head, so the opening between the jaws is centered, but the handle may instead connect to any portion of the head so the gap or opening is oriented in a different direction
In another embodiment, the wrench may be a socket member, with a tab that is adapted to receive a socket wrench square drive or hex drive. Alternatively, it may have a male hex or other member to receive a female drive.
The smooth or toothless arcuate surface between the two second teeth lets the wrench operate as a spanner, and also lets the wrench accommodate either a six- or an eight-lug lock nut. The arcuate surface fits up against the outer edges of the lugs, and lets the wrench teeth lever against the captured lugs of the lock washer.
Preferably, the wrench handle is covered with an insulating plastic coating. The wrench is manufactured, e.g., by laser cutting a sheet of a suitable steel, and this allows the handle, jaws and teeth to be of a uniform thickness. The inwardly directed teeth do not slip off the lock nut while it is being turned. The offset can be created with a bending press.
The above and many other objects, features, and advantages of this invention will become apparent from the ensuing description of a selected preferred embodiment, which is to be considered in connection with the accompanying Drawing.